1. Field of the Invention
The present invention relates to an image sensor, and more particularly, to an image sensor for detecting a wide spectrum, in order to effectively detect various visible and infrared spectrum and accordingly enhance photoelectric conversion efficiency.
2. Description of the Related Art
In general, an image sensor is an electrical device for converting an optical image, that is, changes in light, into an electrical signal, and is used widely in mobile phones, digital still cameras, personal digital assistants (PDAs), toys, electronic games, robots, personal computer cameras, optical computer mice, office scanners, security surveillance cameras, night infrared cameras, recognition systems, biometric systems, wireless endoscopes, etc.
Meanwhile, one of various methods for obtaining visible images is to obtain visible color images in a visible region having wavelengths of 400 through 700 nm using a TV camera, etc.
For example, there has been developed a method of capturing red/green/blue (RGB) images at different times by rotating a color filter wheel and then combining the RGB images, a method of separating light into its spectral components using an optical spectroscope and a plurality of image sensors (generally, three RGB image sensors) to distinguish colors apart, and a method of representing colors through a single image sensor using a Bayer pattern invented by Dr. Bayer. The method using the Bayer pattern, among the methods, has low color reproducibility compared to the other two methods. Recently, a method of representing colors using the fact that the depth of silicon in which light is permeated depends on the wavelength of the light has been proposed.
In the above-described methods, the reason of creating a color image by separating RGB colors from each other, detecting and then combining the RGB colors upon viewing is because the shape and color of an object depend on the wavelengths of RGB colors. That is, an object has its intrinsic apparent characteristics in various wavelengths regions which also extend beyond the visible light region.
Accordingly, when a target object is measured in various optical regions having different spectrums, such as ultraviolet rays, near-infrared rays and infrared rays, as well as visible rays, more information about the target object can be obtained. That is, a color can be defined as a combination of two or more pieces of wavelength spectrum information, instead of as a simple RGB combination. In this case, images which are different from those which human eyes sense may appear, but such images will contain useful information when they are applied to an automated imaging system such as a machine vision system.
In general, a part of ultraviolet rays, visible rays, and near-infrared rays having wavelengths shorter than 1 μm, are sensed by a silicon-based image sensor, and infrared rays having wavelengths longer than 1 μm are sensed by an image sensor made of InSb, MCT, etc.
In order to create multichannel images using the above-described methods, different cameras including different image sensors and different technologies are needed.
However, in the case where two or more image sensors or cameras are used, a serious problem occurs in an optical arrangement upon manufacturing the image sensors or cameras, and mechanical/thermal/optical distortion is generated due to environmental factors. Accordingly, an electrical/mechanical/optical system for compensating for such mechanical/thermal/optical distortion is needed, which results in an increase of cost.